1. Technical Field
The present invention relates to a method and an apparatus for ejecting liquefied material.
2. Related Art
As a replacement of conventional injection methods, a method that employs a droplet ejection apparatus has been known, which apparatus ejects droplets of liquid crystal material into a space defined by a seal material on a glass substrate before bonding of the glass substrate has been known.
This type of droplet ejection apparatus includes a mother glass substrate mounted on a stage, a droplet ejection head through which liquid crystal in the form of droplets is ejected into respective cells formed on the mother glass substrate in a matrix-like manner, and a mechanism that moves the mother glass substrate and the droplet ejection head relative to each other in a two-dimensional manner. Specifically, a predetermined amount of liquid crystal in the form of a droplet is ejected from the droplet ejection head and received in a rectangular frame-like seal member arranged in each of the cells. In such ejection, the amounts of the liquid crystal received in the cells must be all equal. The mother glass substrate and an opposing substrate are bonded together and subsequently cut apart into pieces in correspondence with the cells. In this manner, a plurality of liquid crystal panels are manufactured.
The liquid crystal exhibits high viscosity at normal temperature. Thus, if the liquid crystal is ejected from the droplet ejection head at normal temperature, the weight of the liquid crystal ejected cannot be uniform for each of cycles of ejection. In this case, the amounts of the liquid crystal ejected into the respective cells become nonuniform. Depending on the type of the liquid crystal, clogging may occur in the droplet ejection head. Japanese Laid-Open Patent Publication No. 2003-19790 discloses a droplet ejection apparatus having a heating member that heats liquid crystal supplied to a droplet ejection head. Such heating lowers the viscosity of the liquid crystal and thus the droplet ejection apparatus ejects the liquid crystal with a lowered viscosity. Operation of the heating member is controlled by a controller in such a manner that the liquid crystal in the droplet ejection head is constantly maintained at a predetermined temperature.
However, if the liquid crystal is ejected onto the cells on the mother glass substrate after the liquid ejection head is moved from a standby position spaced from the mother glass substrate to a predetermined position above the mother glass substrate, the liquid crystal is ejected onto the cells by decreased amounts at an early stage of ejection, compared to the liquid crystal ejected at later stages of the ejection.
Specifically, the temperature of the liquid crystal in the droplet ejection head is adjusted in correspondence with the temperature in the proximity of the ejection head so as to be maintained at a predetermined temperature. Since temperature changes in the proximity of the standby position changes are small, the longer the time in which the droplet ejection head is held at the standby position, the more stable the temperature of the liquid crystal in the droplet ejection head becomes.
However, the atmosphere in which the liquid ejection head is located at the standby position is different from the atmosphere in which the liquid ejection head is arranged on the mother glass substrate. Thus, the temperature of the droplet ejection head is lowered by the time ejection of the liquid crystal is started after the droplet ejection head has been moved from the standby position to the position above the mother glass substrate. That is, heat balance in the droplet ejection head and the proximity of the droplet ejection head is maintained in a stable state as long as the droplet ejection head is held at the standby position. However, as the droplet ejection head is moved to the position above the mother glass substrate, the heat balance in the droplet ejection head and the proximity of the droplet ejection head abruptly and greatly changes. If the droplet ejection head is maintained above the mother glass substrate for a long time, the heat balance in the droplet ejection head and the proximity of the droplet ejection head becomes stabilized. Thus, the temperature in the droplet ejection head is adjusted stably on the mother glass substrate. However, at the aforementioned early stage of the ejection, great change of the viscosity of the liquid crystal is caused by the abrupt change of the heat balance. This decreases the amount of the liquid crystal supplied to each of the corresponding cells at the early stage.
Further, since the nozzle plate of the droplet ejection head is formed by an extremely thin metal plate, heat produced by the liquid crystal in the droplet ejection head is easily dissipated through the nozzle plate. This further decreases the amount of the liquid crystal supplied to each of the corresponding cells at the early stage of the ejection.